1. Technical Field of the Invention
The present invention relates generally to measuring tools and devices, particularly to leveling devices. More particularly, the present invention relates to a spirit level adapted with a mechanism for use in determining a minimum satisfactory inclination.
2. Background Information
Spirit levels, such as torpedo-type levels, are commonly used in a number of different technical fields including plumbing, installation of electrical conduit, sheetmetal fabrication and others. Such levels typically are small, and are therefore quite portable. Many such levels are small enough to fit easily into a pocket. Their small size also makes torpedo levels easy to use in close quarters where a box-style or I-beam level would be unwieldy and inconvenient. Torpedo levels are suitable for measuring bend angles or other similar functions where absolute precision of a vertical, horizontal, or angled line is unnecessary.
In one application, a torpedo level may be used to determine a small angle of inclination, such as the desired inclination of a pipe for draining wastewater or sewage. The inclination for such a pipe is typically a 1 to 2 degree angle. One common method of determining the inclination in this application is measuring the length of pipe versus the drop. For example, to obtain an inclination of about 1 degree, a pipe must drop about 0.25 inches per 12 inches (1 cm per 48 cm) of length. This is presently a fairly complicated process, using both hands and one or more tools.
One prior art leveling device, U.S. Pat. No. 4,653,193, attempted to address this problem by adding ramp structures to the sides of a torpedo level. The ramp structure inclines the level relative to a pipe when the level is laid on its side on the pipe. If the pipe is thereafter moved to bring the level to horizontal, the pipe assumes the ramp's inclination angle, which is the desired angle for mounting the pipe. The ramp on each side is not retractable or removable. This property diminishes one's ability to use the sides of the level as a straight edge for marking, may hamper storage or easy removal from storage, and may easily become damaged, broken, or worn down during normal use.
Another prior art leveling device, Great Britain Patent Application No. 2,276,451 attempted to address this problem using a scale means and reversibly movable member such as a micrometer screw to indicate a value based on a distance from one end of the movable member to an abutment surface. The required scale means is preferably calibrated to indicate an inclination as a vertical to horizontal ratio. The adjustable scale means requires looking at the scale and a finer adjustment than a step-wise adjustable movable member with pre-set increments that do not require looking at a scale.